The invention concerns a fifth wheel coupling for the articulated connection of a tractor to a semitrailer, with a fifth wheel coupling plate resting on the double train, which has at least one arc-shaped sliding lining as bearing surface, secured to the coupling plate without twisting.
Fifth wheel couplings are used for form-fitting, yet articulated connection of a tractor to a semitrailer, which then together form a so-called double train. The fifth wheel coupling has a fifth wheel plate with a V-shaped or mouthlike insertion cutout, also known as the coupling or capture mouth, which is bounded on both sides by a somewhat downward sloping horn. The insert cutout, the coupling mouth, passes into a central recess, in which a wearing ring can be arranged. On either side of the wearing ring, there are lock elements, especially a locking hook, which are disengaged from the central recess when the fifth wheel coupling is open. The coupling plate is permanently joined to the frame of the tractor primarily by means of bearing blocks and possibly a mounting plate.
On the semitrailer, at the bottom of the front end, there is an upper plate on which is arranged a downwardly pointing coupling or kingpin. In the coupling process, this pin is guided by the coupling mouth in the coupling plate and inserted into its central recess until it comes to lie against the wearing ring. The upper plate forms, as it were, the counterplate to the coupling plate. As soon as the kingpin lies against the wearing ring, the lock elements are brought into the locking position, whereupon the locking hook embraces the kingpin with form fit, yet able to rotate.
Fifth wheel couplings of the above kind are generally known and are largely standard equipment on double trains (DIN74080=ISO 337).
A significant major problem with such couplings is the friction between the coupling plate and the upper plate, especially because of the constant relative motions between them while traveling on curves, since the coupling plate in normal use is typically secured to the double train and unable to turn about a horizontal axis.
Numerous strategies have been adopted to reduce this fundamentally dictated friction.
One strategy is known to be (DE-PS 25 35 151; EP 0 130 402 B1) to employ a so-called plate lubrication, during which grease is placed between the two plates at regular, relatively short maintenance intervals.
As an alternative or to supplement the plate lubrication, there are known fifth wheels (DE 35 30 467 A1; EP 0 117 319 B1; DE 44 18 533 C2; DE 296 03 641 U1), in which a coating or fastening of antifriction materials to the coupling plate is provided. Usually these antifriction materials have the form of arc-shaped sliding coatings which preferably consist of plastic and which are embedded in corresponding recesses in the metallic collective coupling plate and secured there. The sliding layer can be bent like a horseshoe or have two or more approximately semicircular sliding layers, as in the case of the aforesaid DE 296 03 641 U1, which are screwed together with the coupling plate.
In such fifth wheels with sliding linings screwed onto the coupling plate, the following problems occur.
Since the sliding lining projects above the metallic coupling plate, so that the semitrailer with its upper plate can slide on it, the fastening screws of the sliding lining are heavily exposed to shear force due to the turning during operation of the semitrailer, so that under certain circumstances the fastening screws can break off.
The material of the sliding lining generally has a coefficient of thermal expansion higher than steel, the material from which the coupling plate itself is made. By the action of heat, e.g., by the sun or by high outdoor temperatures when using semitrailers in hot regions, the sliding lining then expands very greatly, which results in an additional mechanical loading of the fastening screws.
To address this problem, the aforesaid DE 296 03 641 U1, on which the invention is based, calls for making the surface of the cavity somewhat larger than is necessary to accommodate the sliding lining. Therefore, although the sliding lining can expand without being exposed to high stresses and breaking apart, the mechanical loading of the fastening screws still remains.
Even though the edges of the recess in which the sliding lining is embedded will absorb extreme transverse forces acting on the sliding linings, since the sliding linings cannot move to the side because of touching the inner wall of the recess, this effect only sets in when the movement has overcome the expansion gap, so that the heavy shear load on the fastening screws remains.
A form-fitting connection between sliding lining and coupling plate which prevents turning and allows a limited mobility is described in U.S. Pat. No. 5,482,308 and in EP 0 792 793 A2.
In U.S. Pat. No. 5,482,308, the connection is realized by a trapezoidal overlapping of the coupling plate with the sliding plate and also by wedges which run from the side of the sliding lining into the edge of the coupling plate. The trapezoidal projections of the sliding lining must be secured by means of trapezoidal fastening blocks and screws, for example. This makes it very time consuming to assemble the coupling plate or replace the sliding lining. During shear or thermal expansion, the forces primarily attack the trapezoidal projections, where material fatigue thus occurs rapidly.
In EP 0 792 793 A2, the sliding lining has bulges on the underside, which are form-fitted to complementary openings in the coupling plate. The coupling plate and the sliding lining are further held together by a screw passed through and a locking nut. Additional components are urgently needed for the fastening, such as a screw with locking nut. This increases the outlay when assembling the coupling plate or changing the sliding lining. Furthermore, at the fastening points the material wear is greatly increased by shear forces or thermal expansion of the sliding lining.
The purpose of the invention is to configure the above-designated fifth wheel such that a secure and thermally expandable fastening of the sliding lining is assured, even under strong shear forces.
The invention accomplishes this in that form-fitted connection elements on the underside of the sliding lining are formed as lands extending radially outward from a virtual midpoint in the opening of the coupling plate and the form-fitted connection elements are formed on the upper side of the coupling plate as grooves complementary to them.
The form-fitted connection, properly configured, absorbs the shear forces and thanks to the mutual movability of the connection elements of the form fit enables a thermal expansion of the sliding plate without noticeable mechanical load on the form-fitted connection.
Because of the radial direction of the lands and grooves in relation to the virtual midpoint of expansion in the central opening, the sliding lining can expand in the radial direction, without the form fit being impaired by this.
Since the lands/grooves run perpendicular to the applied rotational forces, i.e., the direction of rotation of the coupling plate, the sliding lining is protected against twisting, and the form-fitted connection naturally absorbs the transverse forces.
Thanks to the rib-like radial lands on the sliding lining, a stiffening of the sliding plate is achieved at the same time. This, in turn, can substantially diminish the wall thickness locally between the ribs, the lands, and this in turn can advantageously reduce the structural height of the fifth wheel and the weight of the sliding lining.
In order to ensure a secure form fit during use, according to another embodiment of the invention hold-down elements are provided in the form of screws, which join the sliding lining to the coupling plate without absorbing shear forces.
Therefore, in this case the screws only have the function of a securing, but no longer need to take up any forces. They can thus be dimensioned accordingly with less strength.
Alternatively, according to another embodiment of the invention, in order to ensure a secure form fit during use, hold-down elements in the form of clip-like, elastically flexible detente elements are provided at the free end of the lands, which can engage with the grooves of the coupling plate. The detente elements can thereby form a bulge or an outer collar.
In such an embodiment, the mounting of the sliding lining is also advantageously very simple. The sliding lining is simply forced from above with its lands into the grooves of the coupling plate, where the lands then engage to complete the form fit.
In a preferred embodiment, the lands have recesses at the side facing the coupling plate, which serve to accommodate expanding elements, which hold the detente elements in the engaged condition. The depth of the recesses can correspond to the depth of the lands. The expanding elements can be introduced by hand into the recesses and force the detente elements against the coupling plate.
Other advantages and configurations of the invention will result from the description of the sample embodiments presented in the drawings.